**4. Conclusions**

In conclusion, for fresh leaves, November was the best time to obtain extracts richer in simple phenolic compounds, secoiridoids, flavonoids, and triterpenoids as compared to the other sampling times. However, after drying, the behavior of the phenolic compounds and triterpenoids varied according to the drying temperature. In fact, at 25 ◦C, January sampling demonstrated the highest contents of secoiridoids and flavonoids, whereas April showed the highest simple phenolic compounds amounts. On the other hand, when dried at 40 ◦C, leaves collected in November showed the highest amounts in secoiridoids, flavonoids, lignans, and triterpenoids, whereas leaves collected in January and August showed the highest amounts in simple phenolic compounds. The same was observed for secoiridoids and triterpenoids for leaves collected in November at drying temperatures of 60 ◦C and higher. Accordingly, April seemed to be the best sampling time for better recovery of lignans, and August seemed to be the best time for recovering higher simple phenolic compounds at elevated drying temperature.

Among analyzed samples, fresh leaves were generally characterized by higher amounts of flavonoids, lignans, and triterpenoids, whereas secoiridoids were generally found at higher amounts

in samples dried at 120 ◦C. It is noteworthy that samples dried at 120 ◦C and collected in November presented among analyzed samples with the highest amounts in secoiridoids, flavonoids, triterpenoids, and other polar compounds. Since knowing the qualitative and quantitative composition as well as the occurrence of the phytochemicals in a given plant species is a crucial step for investigating the bioavailability and biochemical effect of any dietary phytochemical, and such results would be very useful in the study of the implication of olive leaf phytochemicals in biological activities. In addition, such findings would be helpful in terms of industrial valorization of El Hor olive leaves since it is important to know the best sampling time and drying temperature to obtain the highest yield of compounds of interest. Olive leaf bioactive compounds can be used as an important source to produce nutraceuticals or to be included in functional food thanks to their potential health benefits.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/1996-1073/12/5/947/s1. Statistical data on phenolic and triterpenoid compounds determined according to the drying temperature and sampling season.

**Author Contributions:** Investigation, A.T., J.L.Z. and H.J.; Methodology, A.T. and J.L.Z.; Supervision, J.L.Z., L.A., A.S.C., D.A.R. and J.Y.C.; Validation, A.T. and; Writing—Original Draft, A.T., J.L.Z. and N.T.; Writing—Review & Editing; L.A., A.S.C., J.Y.C. and D.A.R.

**Acknowledgments:** This work was supported by the Tunisian Ministry of Higher Education under the Tunisian-Korean project "Development of Anti-arthritic remedy with Olive by-products".

**Conflicts of Interest:** The authors declare no conflict of interest.
